This is a solid addition to the Spheres of Power (SoP) system, but not quite as good as the core SoP book. Most of the Sphere class archetypes are good, though our group has house rules for some of them, most notably the Sphere Magus. (We let the Magus keep his Arcane Pool, and instead removed the bonus Spell Points.)
The archetypes for the SoP classes are a bit uneven, with some being well-balanced and interesting, while others are just weird.
Still, the PDF is well worth the price if you want to completely replace the magic system with SoP and still use the casting classes from the Advanced Player's Guide, Advanced Class Guide and/or Ultimate Magic.